In a vehicle drive train, various gear ratios may be established in an automatic transmission. A shift point map stores data that relates the transmission gear ratios to various magnitudes of vehicle speed signal and engine load signal. Ordinarily, an appropriate one of the gear ratios to the current vehicle speed and engine load signals is established in the transmission automatically in accordance with the shift point map. A vehicle operator can hardly recognize what gear ratio is established in the transmission, since shift shocks are reduced to an unnoticeable level. Recently, automatic transmissions have been developed, which are operable in a manual shift mode. In such automatic transmissions, the vehicle operator can manually shift from the current gear ratio up or down to the adjacent next gear ratio.
In such manually ratio controlled automatic transmissions, a manually operable select lever has a manual shift mode in addition to an automatic shift mode. This select lever in its manual shift mode has an upshift position and a downshift position. An operator moves the select lever to the manual shift mode and presses the level to the upshift position to produce an upshift demand or to the downshift position to produce a downshift demand. A transmission controller receives the operator upshift or downshift demand and controls a shift from the current gear ratio to the adjacent next gear ratio.